Digital television broadcasting including high-definition television (called HDTV hereafter) has recently enabled providing high-quality sound and video contents that can compare favorably with the originals (such contents are called simply contents hereafter). Further, digital video recorders that have the following features have already become commercial: receiving contents that have been broadcast in digital television broadcasting; and recording the received contents on a hard disc, a rewritable optical disc or the like.
Accompanied by this, protecting the copyright of video contents is increasingly becoming important. For example, in a satellite digital broadcasting and digital terrestrial television broadcasting, a system called “copy-once control” has been implemented in Japan in 2004.
The system of the copy-once control will be described below. First, control signals indicating “capable of being recorded only once” (called copy-once control signals hereafter) are added to sound and video data, and then the resulting data are encrypted. Further, the obtained encrypted digital data are broadcast. At this time, such digital data that are received in broadcasting are allowed to be digitally decoded only once. In other words, the sound and video data to which copy-once control signals are added can be recorded on a recording medium such as a hard disc and a rewritable optical disc. Such copy-once control signals are rewritten as copy-never control signals at the time of recording. Therefore, the resulting signals disable copying the recorded data on another recording medium. However, there is an exception as will be described below. It is allowed to move the recorded data to another recording medium on the premise of deleting or disabling reproduction of the recorded data held on an original recording medium. (For example, refer to the following Reference Document 1.)
Reference Document 1: the eighth part (procedures for protecting contents in digital terrestrial television) Technical data for operating procedures of digital terrestrial television using the one or more pieces of important information for reproduction included in the read reconstruction information represented by ARIB TR-B14. ARIB is an abbreviation for “Association of Radio Industries and Businesses, and ARIB TR-B14 is a technical document distributed by the ARIB.
Here is an example case of receiving contents protected by copyright via digital television broadcasting and directly record the contents on a first recording medium such as a rewritable optical disc using the above-mentioned conventional technique. In this case, the reproduction of the contents is disabled on the first recording medium but the contents are not rewritten. Such contents cannot be recorded by a recording and reproducing apparatus, but they may be read out by using a drive of a personal computer. In other words, there is a fear that such contents are illicitly copied. Here is another example case of rewriting the contents on the first recording medium in order to disable reproduction at the time of moving the contents from the first recording medium to a second recording medium. In this case, the contents must be written back from the second recording medium at the time of the recovery of the contents on the first recording medium, which causes problems that it takes very long time and that the processing load increases.
Also, a conventional recording and reproducing apparatus that can perform a copy-once control moves contents to an external recording medium such as an optical disc. Therefore, in the case of moving the contents to a recording medium whose capacity is limited, compression coding may be performed on the sound and video data again in order to decrease the data rate, and then such sound and video data may be moved on it. In the case of moving contents in a decreased data rate and once rewriting the data of the contents in order to disable reproduction causes a problem that the original reproduction quality of the contents cannot be recovered any more.